Just going to speak from experience here....
My first gun ever was the TM Socom Mk23 NBB. All the guys from the old Windsor Airsoft Club can attest to the fact that their paranoia on the field went up excessively when I was out there with that. That little gun fired 330fps out of the box and the suppressor on it ACTUALLY FUCKING WORKS. It's goddamn hard to hear firing more than 30 feet away and it's ridiculously accurate for a pistol.
One favourite moment with it is the time I took out 3 guys in an advancing squad with it before the rest of them realized they were under fire.
So yes, in my experience even outdoors a pistol CAN be a viable option for a primary weapon, but I don't think there are many handguns that have the performance characteristics of the Socom Mk23 NBB.
Age Verifier - Lower Vancouver Island
Brotherhood of Nod - Nod Prime || Vancouver Island Airsoft League - President